This application claims the priority of German patent Application No. 100 13 270.7 filed Mar. 17, 2000, which is incorporated herein by reference.
The invention relates to a fluid-operated percussion device having a percussive piston, which moves in a work cylinder and strikes a tool, and a control having a slide valve, which moves in a pilot valve. The percussive piston has two piston surfaces of different sizes, with the smaller piston surface, which is effective in the direction of the return stroke, being continuously connected to a pressure line that is acted upon by the work pressure, and the larger piston surface, which is effective in the direction of the work stroke, being alternately connected via the pilot valve to the pressure line and a pressureless return line. The slide valve has two valve surfaces that are of different sizes and are effective in opposite directions of movement, with the smaller valve surface, which acts on the slide valve in the direction of the return-stroke position of the slide valve, being continuously connected to the pressure line, and with the larger valve surface being alternately connected temporarily to the pressure line and to the return line via a circumferential groove disposed between the piston end surfaces.
The German Published Patent Application DE 196 36 659 A1 describes a percussion device of the generic type mentioned above.
The known percussion device is embodied such that the pilot valve is switched into the return-stroke position when a percussive-piston limit position is exceeded in the direction of the work stroke. During the return stroke, which follows immediately thereafter, a short-stroke line is acted upon by pressure, which prematurely displaces the pilot valve into the work-stroke position, so the percussive piston only executes a short stroke. In the event that the tool cooperating with the percussive piston penetrates the material to be comminuted, and the percussive piston leaves its normal striking plane, the automatic change in stroke reduces the energy for individual strikes.
Depending on the working and application conditions, it may be desirable to equip fluid-operated percussion devices with a no-load-strike safeguard, especially from the standpoint of avoiding an undesired stress or the ensuing damage. The Japanese Published, Non-Examined Patent Application Hei10-80878 of Mar. 31, 1998, proposes such a solution within the scope of a hydraulic striking device.
In the described hydraulic striking device, a short-stroke input disposed on the work cylinder of the percussive piston is connected via a stroke-reversing valve to a valve-control circuit and to a high-pressure circuit, which allows the function of the striking device to be influenced as a function of the position of the stroke-reversing valve, for avoiding no-load strikes.
The stroke-reversing valve associated with the short-stroke input can assume either a no-load-prevention position or a normal-operation position. In the first position, the work pressure present in the high-pressure circuit is applied to the short-stroke input. In contrast to this, in the normal-operation position, the connection between the short-stroke input and the high-pressure circuit is broken, which may cause the known striking device to function in short-stroke operation.
Based on the association of the stroke-reversing valve with the short-stroke input, it is impossible to also prevent the execution of no-load strikes, regardless of the effect of the short-stroke input.
It is therefore the object of the invention to modify the generic percussion device such that the percussive piston is shut down, regardless of other control-related circumstance if it has reached a predetermined extended position in the direction of the work stroke.
The above object generally is achieved according to the present invention by a fluid-operated percussion device comprising:
a percussive piston that moves in a work cylinder and strikes a tool, with the percussive piston having two opposed piston end surfaces of different sizes, with the smaller piston surface, which is effective in the direction of a return stroke, being continuously connected to a pressure line that is acted upon by a work pressure, and with the larger piston end surface, which is effective in the direction of a work stroke, being alternately connected via a pilot valve to the pressure line and to a pressureless return line;
a control having a slide valve that moves in a pilot valve, said slide valve having two valve surfaces that are of different sizes and are effective in opposite directions of movement, with the smaller valve surface of the slide valve, which smaller valve surface acts on the slide valve in the direction of the return-stroke position of the slide valve, being continuously connected to the pressure line, and with the larger valve surface of the slide valve being alternately connected temporarily to the pressure line and to the return line via a circumferential groove disposed on the surface of the piston between the piston end surfaces;
the interior of the work cylinder additionally has a no-load-strike opening, which is enabled, in the direction of the interior, by a front piston collar of the percussive piston, which front piston collar has the smaller piston surface, after the percussive piston has overshot an extended position occurring in normal operation by a predetermined distance in the work-stroke direction to assume a no-load-strike position;
a safety element, which can be switched between a first inoperative end position and a second operative end position and whose input side is connected to the pressure line, is disposed upstream of the no-load-strike opening, with the safety element acting on the no-load-strike opening with the work pressure originating from the safety element in the second operative end position, and with the safety element breaking the connection between the pressure line and the no-load-strike opening in the first inoperative end position; and
when the safety element assumes the second operative end position and the percussive piston reaches the no-load-strike position, the work pressure applied to the no-load-strike opening acts on the control via the circumferential groove such that the slide valve of the control is blocked in the work-stroke position.
As can be seen from the above, the invention proposes to additionally provide the interior of the work cylinder that receives the percussive piston with a no-load-stroke opening, which opening is only enabled in the direction of the interior by the front piston collar of the percussive piston, which collar has the smaller piston end surface, after the percussive piston has overshot the extended position occurring in normal operation by a predetermined distance in the direction of the work stroke to assume a no-load striking position.
Additionally, a safety element that can be switched between two end positions, i.e., an operative position and an operative position, and whose input side is connected to the pressure line having the work pressure is disposed upstream of the no-load-strike opening, with the no-load-strike opening being acted upon by the work pressure originating from the safety element in the operative position, and with the safety element breaking the connection between the pressure line and the no-load-strike opening in the inoperative position.
Depending on the predetermined structural conditions, within the spirit of the invention, the additional no-load-strike opening can be displaced further in the direction of the tool. In other words, it is located closer to the tool than the opening of a likewise provided short-stroke line, when seen in the axial direction of the percussive piston.
If the safety element assumes the operative position, and the percussive piston has reached the no-load-strike position, the work pressure applied to the no-load-strike opening acts on the control via the circumferential groove disposed between the two piston collars of the percussive piston such that the slide valve of the control is blocked in the work-stroke position. The work pressure applied to the no-load-strike opening prevents the control from switching from the work-stroke position into the return-stroke position, so the percussive piston cannot move in the direction of its return stroke. Consequently, the percussion device is shut down, and can only be restarted through the mechanical lifting of the percussive piston, i.e., the pressing of the percussive piston against the tool.
Of great significance for the invention is the fact that an effective no-load-strike opening in terms of control is additionally present, whichxe2x80x94regardless of the conditions in long- and/or short-stroke operationxe2x80x94allows the percussive piston to be shut down after it has attained a deviating no-load-strike position. Unlike in the state of the technology cited at the outset, the switchable safety element cooperating with the no-load-strike opening is not connected to the opening of a short-stroke line that may be present.
Correspondingly, the percussion device embodied according to the invention can also be safeguarded against no-load strikes if it is possible to switch between long- and short-stroke operation.
As already mentioned, the position of the no-load-strike opening can be defined by the fact that it is located closer to the tool (seen in the axial direction of the percussive piston) than the preceding opening into the interior of the work cylinder, by way of which the control is influenced by the switch between the work-stroke position and the return-stroke position.
The subject of the invention can be modified in that the breakable connection between the safety element and the no-load-strike opening is located inside a housing that represents at least one component of the work cylinder.
The breakable connection can either be disposed inside its own housing, which is in turn connected to the work cylinder, or be located directly inside the work cylinder itself.
Provided that the safety element meets the other aforementioned requirements, it can have an arbitrary embodiment and location. The safety element preferably constitutes a detachable component, which is essentially disposed inside the housing or the work cylinder, and is accessible from the outside of the percussion device. In this way, the safety element is additionally protected against external influences, particularly damage.
A simple embodiment variation of the invention is for the safety element to be embodied as a rotary slide valve. This valve need only be embodied and disposed such that its predetermined end position (inoperative position and operative position, respectively) is not changed by external influences.
In particular, the rotary slide valve can include a screw-in hollow cylinder and an adjusting pin with a connecting conduit, the pin being rotatably held inside the hollow cylinder. Depending on the rotational position of the adjusting pin, a connection can be produced between the no-load-strike opening and the pressure line, with the adjusting pin being clamped to the hollow cylinder in order to fix its rotational position.
Within the spirit of the invention, the safety element can also have a latching pin, which can be secured in numerous positions inside the component that receives it (housing, work cylinder). A connection is either present between the pressure line and the no-load-strike opening in a first latched position, or is broken in a second latched position. Furthermore, the safety element can be embodied such that the latching pin can be displaced longitudinally between the latched positions, counter to the effect of at least one split washer serving as a counterbearing.
In a further advantageous embodiment of the subject of the invention, the safety element has a threaded pin that is accessible from the outside of the component that receives it (housing, work cylinder) and is screwed to the component, as well as an exchangeable pin that can be fixed inside a receiving bore by the threaded pin. The exchangeable pin is either embodied as a bridge element, which connects the no-load-strike opening to the pressure line, or represents a blocking element that blocks the connection between the pressure line and the no-load-strike opening. Depending on the operating conditions of the percussion device, it is thus possible to switch the no-load safety element to be operative or inoperative simply by exchanging the exchangeable pin. The advantage of this embodiment is that the operating mode of the percussion device that is predetermined by the insertion of the exchangeable pin cannot be subjected to any undesired changes.
The invention is described in detail below in conjunction with schematic drawings of exemplary embodiments.